Photographic objective with four air-spaced singlets

ABSTRACT

PHOTOGRAPHIC OBJECTIVE, ESPECIALLY TELEPHOTO OBJECTIVE, WITH FOUR AIR-SPACED SINGLETS FORMING A FRONT GROUP AND A REAR GROUP, THE FRONT GROUP CONSISTING OF A BICONVEX FIRST LENS AND A BICONCAVE SECOND LENS, THE REAR GROUP CONSISTING OF A THIRD LENS IN THE FORM OF A NEGATIVE MENISCUS AND A FOURTH LENS IN THE FORM OF A POSITIVE MENISCUS.

\Jllllvwu Uuvv [U] [72] inventors Walter 350/221 Klaus Elle, bad Kreuznach, Germany [2|] Appl. No. 842,945 References Cited [22] Filed July 18, 1969 UNITED STATES PATENTS i 1 Pmmd 181 2,390,387 12/1945 Rayton et al 350/221 1 Assam 1 81 o 1 Werke 2,818,776 1/1958 Hayes et al. 3so/221x Km W Gmuy Primary Examiner-David Schonberg [32 1 priority In]! 19 968 Assistant Examiner-Paul A. Sacher [33] m Attorney-Karl F. Ross s1 1317972794 mommmc om mm mm ABSTRACT: Photographic objective, especially telephoto objective, with four air-spaced singlets forming a front group and g a rear group, the front group consisting of a biconvex first lens [52] US. Cl. 350/221 and a biconcave second lens, the rear group consisting of a [51] Int. Cl. G02b 9/36, third lens in the form of a negative meniscus and a fourth lens G02b 9/56 in the form of a positive meniscus.

PATENTEU JUN28 I97:

d5 d6 d7 L3 WALTER WCSLTQHE KLAUS EL Inventors 'flr {Kw Attorney PHOTOGRAPHIC OBJECTIVE WITH FOUR AIR-SPACED SINGLETS Our present invention relates to a photographic (or cinematographic) objective of the type wherein four air-spaced meniscus-shaped third lens L3 of dispersive character with radii r5, r6 and thickness d6, and a meniscus-shaped fourth lens L4 of collective character with radii r7, r8 and thickness singlets, Le. a positive first lens, a negative second lens, a nega- 5 I tive third lens and a positive fourth lens, define a front group The fi" Space sepal'mmg the lenses Ll 15 a and a rear group separated from each other by a diaphragm small fl'acuon of the diaphragm P? sePal'aung h space which is large compared with the air spaces separating groups L2 L4; the last P? P the two lenses f each group lenses L3 and L4, [5 an even smaller fraction of air space d2.

The general object of the present invention is to provide an objective of this character, especially a telephoto objective, y: gsyz gggihg i gzg g f z mortispemfic fugue adapted to be used with relative apertures on the order of emngo lmage curva o can best be realized if the surface powers An/r of the inl:6.3 to l:4.5 and with field angles up to about :l7 with good cc of both mired dent and angled: ndcm dividual lens surfaces rlr8 fall within the following ranges, 223 32 ape Pc 5 with the respective surface radius r given in terms of the A more specific object of our invention is to provide an obfocal length I of the system assumed to have value ofunity. JCCUVC of this description in which the field curvature 1S minimized, with attainment of a Petzval radius in a range of i7 +24 to +31 to 33 times the overall focal length. to +03 In accordance with our present invention, the diaphragm r3 to space between the two lens groups exceeds by an order of magnitude the air space separating the lenses of the front ,5 .39 m 2 group (specifically by being about 7 to 13 times as large as the +09 to latter air space) whereas the last-mentioned air space, in turn, ,7 3 to o exceeds by an order of magnitude the air space separating the to lenses of the rear group (specifically by being about 25 to 33 times as large as the gap between the third and fourth lenses). By way of more specific example, we shall now give the Advantageously, pursuant to another feature of our invention, parameters of four representative lens combinations whose the first lens is a biconvex member with a nearly planar rear surface powers fall within the ranges indicated above and surface, the second lens is a biconcave member with a front which define objectives with an overall focal length f=l (mea-. surface less strongly curved than its rear surface, the third lens sured in arbitrary linear units).

TABLE I Abbe Surface Thicknesses and Refractive Numbers, Powers, Lens Radii Separations Indices, n, v. An/r r1= +0.20485 +3. 04056 d1=0.05013 1. 62286 60.06 r2= -2.27135 +0. 27416 d2=0.02005 Air space r3= -0.95746 -0. 70775 L2 d3=0.01404 1. 67764 31. 97 1.68638 d4= 0.24062 Diaphragm space r5= -0.12450 -4. 16643 L3 d5=0t01003 1. 51872 63. 96

d6=0.00060 Air space r7= 1.92094 0. 33654 L4 d7= 0.03008 1. 64647 47. 66

is a forwardly concave negative meniscus, and the fourth lens is a forwardly concave position meniscus whose front surface is more strongly curved than the confronting rear surface of the third lens.

The foregoing objective has a relative aperture of 1:6.3 and is corrected for a field angle of :l5; its back-focal length is 0.5104 linear units. With an actual focal length f of 500 mm., it is suitable for an image size of I X40 mm.

The sole FIGURE of the accompanying drawing shows, diagrammatically, an objective according to our invention including a biconvex first lens Ll with radii r1, r2 and thickness d1, a biconcave second lens L2 with radii r3, r4 and thickness 03, a

The foregoing objective has a relative aperture 6r": 55165116 is corrected for a field angle of :1 6.5; its back-focal length is 0.4857 linear units. With an actual focal length f of 240 mm.,

75 it is suitable for an image size of Xl20 mm TABLE 111 Air space 1.74703 Diaphragm space Air space The foregoing objective has a relative aperture of l:4.8 and is corrected for a field angle of :13"; its back-focal length is 0.4428 linear units. With an actual focal length f of 210 mm., it is suitable for an image size of 60 X90 mm.

We claim:

1. A photographic objective consisting of four air-spaced singlets including a positive first lens L1, 3 negative second lens L2, a negative third lens L3 and a positive fourth lens L4, said first and second lenses forming a front group, said third and fourth lenses forming a rear group, said front and rear groups being separated by an air space exceeding by an order of magnitude the air space separating said first and second lenses, the last-mentioned air space exceeding by an order of magnitude the air space separating said third and fourth lenses; the numerical values of the radii r1 to r8 of said lenses L1 to L4, their thicknesses and separations d1 to :17, their refractive indices 1:, and their Abbe numbers v, being substantially as given in the following table.

2. A photographic objective consisting of four air-spaced singlets including a positive first lens L1, a negative second lens L2, a negative third lens L3 and a positive fourth lens L4, said first and second lenses forming afrom group, said third and fourth lenses fonning a rear group, said front and rear groups being separated by an air space exceeding by an order of magnitude the air space separating said first and second lenses, the last-mentioned air space exceeding by an order of magnitudc the air space separating said third and fourth lenses;

the numerical values of the radii r1 to r8 of said lenses L1 to L4, their thicknesses and separations d1 to 07, their refractive indices n, and their Abbe numbers v, being substantially as given in the following table:

. -ibbe Numbers, in

Surface Powers. An/r 3. A photographic objective consisting of four air-spaced singlets including a positive first lens Ll, a negative second lens L2, a negative third lens L3 and a positive fourth lens L4, said first and second lenses forming a front group, said third and fourth lenses forming a rear group, said front and rear groups being separated by an air space exceeding by an order of magnitude the air space separating said first and second lenses, the last-mentioned air space exceedingby an order of magnitude the air space separating said third and fourth lenses;

the numerical values of the radii r1 to r8 of said lenses L1 to L4, their thicknesses and separations all to (f7, their refractive indices n, and their Abb numbers v, substantially as given in the following table:

4. A photographic objective consisting of four air-spaced singlets including a positive first len's Ll. a negative second lens L2, a negative third lens L3 and a positive fourth lens L4, said first and second lenses forming a front group, said third and fourth lenses fonning a rear group. said front and rear groups being separated by an air space exceeding by an order of magnitude the air space separating said first and second lenses, the last-mentioned air space exceeding by an order of magnitude the air space separating said third and fourth lenses;

the numerical values of the radii rl to r8 of said lenses L1 to L4, their thicknesses and separations d1 to d7, their refractive indices )1, and their Abb numbers v, being substantially as given in the following table: 

